All-electric measurement of spin texture used for spin current generation will contribute to easier and cheaper way of developing spintronic devices
The magneto-resistance effect is the tendency of a material to change the value of its electrical resistance in an externally-applied magnetic field. It has been widely utilised for applications in sensors and hard disk reading heads.
Figure: (a) Schematic diagram illustrating the Dirac cone of a topological insulator. (b) Spin-momentum locked surface state with hexagonal warping. (c,d) Hall bar device of topological insulator Bi2Se3 for harmonic resistance measurements. (e) Second harmonic resistance signal for the three scans of magnetic fields in xy, zy, and zx planes.
Credit: National University of Singapore
So far, no link has been established between the existing magneto-resistances and spin texture of spin-polarised materials. Researchers from the National University of Singapore (NUS) have recently made a breakthrough in this field, revealing a close relation between the spin texture of topological surface states (TSS) and a new kind of magneto-resistance.
This fundamental advancement is achieved in collaboration with researchers from the University of Missouri, United States. The research team observed for the first time a novel magneto-resistance in three-dimensional (3D) topological insulators (TIs), which scales linearly with both the applied electric and magnetic fields, and shows a close link to the in-plane and out-of-plane spin textures of TSS. The team's finding could help in addressing the issue of spin current source selection often faced in the development of spintronic devices.
The research team, led by Associate Professor Yang Hyunsoo from the Department of Electrical and Computer Engineering at the NUS Faculty of Engineering, published their findings in the journal Nature Physics.
New magneto-resistance found in 3D TI
The discovery of 3D TIs has generated great interest among international researchers to understand the physical properties of this new state of matter, and exploring its applications in optoelectronics and spintronics. So far, the magneto-resistances found in 3D TIs is current-independent, reflecting a linear response of the electron transport to an applied electric field. At the same time, a transport obstacle exists in detecting the surface properties, due to the significant bulk contribution, which overwhelms the surface responses.
"In this work, we observed the second order nonlinear magneto-resistance in a prototypical 3D TI Bi2Se3 films, and showed that it is sensitive to TSS. In contrast with conventional magneto-resistances, this new magneto-resistance shows a linear dependence on both the applied electric and magnetic fields," said Dr He Pan, who is the first author of the study and a Research Fellow at the Department.
Assoc Prof Yang added, "Theoretical calculations by our collaborators from the University of Missouri revealed that the bilinear magneto-electric resistance originates from the spin-momentum locked TSS with hexagonal warping. From the perspective of the microscopic origin, it is a fundamentally new process regarding the conversion of a nonlinear spin current into a charge current under the external magnetic field."
Novel technique to probe 3D spin texture
Probing the surface spin texture is of critical importance for the development of TI-based spintronic devices. However, the approach performed to date is highly restricted to sophisticated tools such as photoemission spectroscopy.
The novel magneto-electric resistance observed by the research team provides a new route to detect the 3D spin texture in TSS by a simple electric transport measurement without involving any additional ferromagnetic layers. The team's study also revealed the hexagonal warping effect in TSS, which could previously only be determined by photoemission spectroscopy.
Commenting on the significance of the breakthrough, Dr He Pan said, "Our results can be applied to extended families of highly spin-polarised materials, like Rashba/Dresselhaus systems as well as two-dimensional transition metal dichalcogenides with spin-polarised states. It also provides a new route to detect the 3D spin texture of these materials by a simple transport measurement."
Moving forward, Assoc Prof Yang and his team are conducting experiments to increase the magnitude of the novel magneto-resistance by refining the TI materials and film thickness. They are also planning to incorporate and test the technology in different materials. The team hopes to work with industry partners to explore various applications with the novel magneto-resistance.
This research work was supported by A*STAR's Pharos Programme.
Goh Yu Chong | EurekAlert!
Studying electrons, bridging two realms of physics: connecting solids and soft matter
18.02.2020 | Tokyo University of Science
Broadband transmission-type coding metasurface for electromagnetic beam forming and scanning
17.02.2020 | Science China Press
Most natural and artificial surfaces are rough: metals and even glasses that appear smooth to the naked eye can look like jagged mountain ranges under the microscope. There is currently no uniform theory about the origin of this roughness despite it being observed on all scales, from the atomic to the tectonic. Scientists suspect that the rough surface is formed by irreversible plastic deformation that occurs in many processes of mechanical machining of components such as milling.
Prof. Dr. Lars Pastewka from the Simulation group at the Department of Microsystems Engineering at the University of Freiburg and his team have simulated such...
Investigation of the temperature dependence of the skyrmion Hall effect reveals further insights into possible new data storage devices
The joint research project of Johannes Gutenberg University Mainz (JGU) and the Massachusetts Institute of Technology (MIT) that had previously demonstrated...
Researchers at Chalmers University of Technology, Sweden, recently completed a 5-year research project looking at how to make fibre optic communications systems more energy efficient. Among their proposals are smart, error-correcting data chip circuits, which they refined to be 10 times less energy consumptive. The project has yielded several scientific articles, in publications including Nature Communications.
Streaming films and music, scrolling through social media, and using cloud-based storage services are everyday activities now.
After helping develop a new approach for organic synthesis -- carbon-hydrogen functionalization -- scientists at Emory University are now showing how this approach may apply to drug discovery. Nature Catalysis published their most recent work -- a streamlined process for making a three-dimensional scaffold of keen interest to the pharmaceutical industry.
"Our tools open up whole new chemical space for potential drug targets," says Huw Davies, Emory professor of organic chemistry and senior author of the paper.
Superconductivity approaching room temperature may be possible in hydrogen-rich compounds at much lower pressures than previously expected
Reaching room-temperature superconductivity is one of the biggest dreams in physics. Its discovery would bring a technological revolution by providing...
12.02.2020 | Event News
16.01.2020 | Event News
15.01.2020 | Event News
18.02.2020 | Life Sciences
18.02.2020 | Earth Sciences
18.02.2020 | Life Sciences